The present invention relates to a control apparatus and a method for an internal combustion engine (which will be hereinafter referred to as an “engine”), and more specifically relates to a control for suppressing output variations between cylinders and is capable of distinguishing between a deviation in an intake air system and a deviation in a fuel system for each cylinder.
Japanese Patent Application Publication No. 2000-64899 discloses a technique for suppressing variations between cylinders of an engine. According to this technique, an error is calculated between an average that is calculated from the sum of the in-cylinder pressures of all cylinders and an average of the in-cylinder pressure of each cylinder. The amount of fuel supply and the ignition timing are adjusted based on the error thus calculated.
According to the above-referenced technique, variations in the output between cylinders can be suppressed by controlling the fuel supply amount and/or the ignition timing. However, according to this technique, an additional component such as an in-cylinder pressure sensor or the like is required for smoothing output variations of all the cylinders.
Therefore, one object of the present invention is to propose an improved technique that is capable of suppressing variations in the output between cylinders in an easier manner without such an additional component.
Furthermore, variations between cylinders may occur in each of a fuel system and an intake air system. Even when there is no variation in the fuel amount between cylinders, the engine output may vary between the cylinders if there are variations in the intake air amount. On the other hand, even when there is no variation in the intake air amount between cylinders, the engine output may vary between the cylinders if there are variations in the fuel supply amount between the cylinders. In order to more accurately smooth the outputs of the cylinders, it is desirable to identify how much variations there are in each of the fuel amount and the intake air amount.